In computer-assisted surgery (CAS) systems which employ inertial-based or micro-electro-mechanical sensor (MEMS), trackable members continue to be developed. One of the principal steps in navigating a bone with inertial sensors is to determine a coordinate system of the bone relative to the sensors, so as to be able to determine the orientation of the bone. For the tibia, the orientation of the bone may be determined by its mechanical axis.
When traditional optical CAS navigation systems are used, the determination of the tibial mechanical axis can be achieved, for example, by using two optical bone sensors fixed to the bone at spaced apart locations, each optical sensor having six degrees of freedom (DOF) (i.e. 3 DOF in position and 3 DOF in orientation). When using trackable members having inertial sensors in an inertial-based CAS system, however, the inertial sensors do not necessarily provide six DOF. While the missing DOF can be calculated if necessary using integrated gyroscope and accelerometer readings, for example, a simpler and more efficient manner to digitize the mechanical axis of a tibia is nonetheless sought.
Therefore, there remains a need for an improved surgical tool which is used in conjunction with a CAS system in order to digitally acquire the mechanical axis of the tibia using readily identifiable anatomical reference points.